Cathodic protection systems are frequently employed to protect steel or ferrous metals from corrosion when exposed to a corrosive media, such as water or other liquids. In the conventional cathodic protection system, a metal which is electropositive to steel, such as zinc or aluminum, is electrically connected to the steel to provide an electrolytic circuit in which the anode will preferentially corrode to thereby prevent corrosion of the steel base material.
Steel vessels are frequently lined with a corrosion resistant material, such as glass or plastic, in an attempt to minimize corrosion of the steel. However, it has been found that intensified corrosion will occur where the steel base is exposed through defects in the coating or in areas where the coating is damaged. Therefore, cathodic protection systems are frequently employed in conjunction with glass lined vessels, such as water heaters, processing vessels, and the like, to prevent the corrosion of any portion of the steel base exposed through defects in the protective coating.
Recently, liquidified manure has been stored in tanks formed of glass coated steel panels. The liquidied manure is highly conductive, approximately ten times as conductive as water, due to the presence of salts from urine and other conductive solids, with the result that rapid concentrated corrosion can occur in areas where the steel is exposed through defects in the glass coating, or in areas where the coating may have been damaged. It has also been found that the glass coating on the edges of the overlapping plate sections is relatively thin as compared to the coating on the flat surfaces, so that the edges can be subject to galvanic attack due to the high conductive nature of the liquified manure.